Sinclair ZX80 / ZX81 / Z88 Forums

Hello ZX81 warriors.

I just got a couple of ZX81's in US (I am assuming VHF signal), but unfortunately I don't have the usual monitor solutions to test them (no old TV, no VCR, no composite convertors, etc).

I am wondering if any of these little hardware may enable my laptop to display the ZX81 tv signal:

1)
http://www.ebay.com/itm/252368317239

2)
http://www.ebay.com/itm/201403380615

thanks!

Hello and welcome

If the computer can do VHF, there should be a channel switch on it.

Item 1) is no good.
Item 2) is a maybe / long shot. The listing does not say that the device can receive analogue TV.

You need a device that can receive an analogue TV signal. The second problem, is that the first ZX81s were designed to work with black and white / monochrome televisions. ZX81s work well with these sets.

But it's not so simple with colour TVs. They produce a poor contrast, very dark picture on some colour receivers. This was fixed when Sinclair changed the ULA chip to a later revision. This later chip includes the "back porch" waveform in the video signal.

If you can solder, there are modules available from time to time (two different modules from two different sellers, one of which is away at the moment) on www.sellmyretro.com that can allow a ZX81 or TS1000 to produce a cleaned up bright clear monochrome composite video signal that is acceptable to colour receivers. It is then much easier to find a converter so that you can use a VGA monitor/display.

The two modules are:
‬ZX8-CCB (developed from the ZX81-CCP).

ZXVid

Note that I don't sell either of these.
Please ask if you would like more information.

Mark

Thanks!

And how about this one?

3)
http://www.ebay.com/itm/HDTV-HD-LCD-Ana ... 2030392108

Maybe it is a good try for 18.50 including free shipping.

I've checked the ZXVid and the main drawbacks are the price and that you need to solder. I prefer for the moment a non-intrusive technique.

Greets.

There is also the Chroma interface which gives RGB video via a SCART socket.
You could easily make a breakout cable, I don'y think SCART/Peritel is seen often in the US.

http://www.fruitcake.plus.com/Sinclair/ ... erface.htm

-B-

I don't get the point why is so difficult to convert VHF/UHF to composite, I remember back in the VCR era most has VHF/UHF input and composite output, I am right?

Without knowing what computer you have, you probably could use this:

http://www.ebay.com/itm/Coax-Cable-TV-T ... SwrklVMBXz

Also this for the RCA cable to convert one end to coax:

http://www.ebay.com/itm/Eagle-F-Male-to ... xyBvZTV-4U

Any comments?

[edits made]

it is certainly not easy to convert vhf/uhf rf tv to composite - directly, it has to pass through a tuner to convert it to an if of around 39mhz, usually, then amplified and gain-controlled, demodulated, and then amplified again to get to standard video level....i've been trying to find a cheapo/easy way for ages, such as feeding the rf into a almost biassed off transistor(to act as demodulator) but no luck, not enough input amplitude...and amplifying uhf is not easy!

vhf is a bit easier than uhf , so 'might' be more possible to do a cheapie....

@gozzo:

Have you tried any of the hardware I mention?

The one that gammaray points also looks very promising.

@1024MAK:

Do you have any further comments on the hardware that gammaray points?

Greets.

gammaray wrote:Without knowing what computer you have, you probably could use this:

http://www.ebay.com/itm/Coax-Cable-TV-T ... SwrklVMBXz

Also this for the RCA cable to convert one end to coax:

http://www.ebay.com/itm/Eagle-F-Male-to ... xyBvZTV-4U

Any comments?

[edits made]

The tuner/converter linked to above at least sounds like it should work.
You will also need a good quality screened coax phono/RCA to phono/RCA lead (look for one described as a video lead, not a cheaper audio lead).

Mark